The muffler is a very important component part of a motor vehicle. As a result, an improvement on the muffler of the motor vehicle can give an added performance to the motor vehicle. During the operation of an engine, exhaust fume and, noise are produced by the gas explosion taken place in the engine cylinder of the motor vehicle. It is therefore readily apparent that the marketability of the motor vehicle can be greatly enhanced by an improved muffler capable of reducing the noise level of the exhaust fume. In addition, the gas mixture in the intake manifold must be propelled by a pressure source to enter the combustion chamber in which the gas mixture is burned in conjunction with the ignition fire. For this reason, it is necessary that the muffler contains an appropriate return pressure for propelling the fuel mixture into the combustion chamber at the time when the gas explosion has taken place in one cylinder and when the gas explosion has not taken place in another cylinder.
There are several kinds of muffler, which are commonly used in the motor vehicles available in the market place today. These mufflers are described herein after.
As shown in FIG. 1, a prior art muffler 10 is provided in the mid-segment thereof with a gas duct 101. Both gas duct 101 and the muffler 10 are provided with a silencing fiber 102 which is made of a metal or glass fiber material. The gas duct 101 is provided at one end thereof with a gas inlet 103 in communication with the engine, and at other end thereof with a gas outlet 104 for discharging the exhaust fume. The gas duct 101 is further provided in the side wall thereof with a plurality of gas holes 105. When the exhaust fume current produced by the engine is brought into the gas duct 101 of the muffler 10 via the gas inlet 103, the gas noise of the exhaust fume current is alleviated by the silencing effects of the gas holes 105 and the silencing 102. However, it is technically troublesome to provide the muffler 10 and the gas duct 101 with the silencing fiber 102. Moreover, the silencing effect of the silencing fiber 102 is greatly undermined by the fast-moving exhaust fume that is unlikely to move into the silencing fiber 102 via the gas holes 105. As a result, the prior art muffler 10 is not effective in reducing the noise of exhaust fume.
In order to overcome the drawback of the prior art muffler 10 described above, the straight gas duct 101 is modified such that the gas duct 101 is so curved as to enable the exhaust fume to move in a curved path in which the exhaust fume flow is slowed down to an extent that an appropriate back pressure is produced in the gas duct 101, as shown in FIG. 2.
The back pressure serves to propel the fuel mixture from the intake manifold into the combustion chamber at the time when the gas explosion in one of the cylinders has taken place and when the gas explosion in another one of the cylinders has not taken place. However, the technical deficiency of the prior art muffler 10 is not resolved by the curved gas duct 101 in view of the fact that the muffler 10 and the curved gas duct 101 must still be provided there-between with the silencing fiber 102 for deadening noises of the exhaust fume current.
Now referring to FIG. 3 in which an improved muffler 20 is shown. The muffler 20 is provided at one end thereof with a gas inlet 201 in communication with the engine, and at other end thereof with a gas outlet 202. The muffler 20 is further provided therein with a plurality of air chambers 203 which are in communication with one another by gas ducts 204 that are arranged alternatively and provided with a plurality of gas holes 205. Each air chamber 203 is provided in the wall thereof with a noise-deadening fiber 206. As a result, the noise of the exhaust fume current is progressively reduced as the exhaust fume current moves from one air chamber 203 to another air chamber 203. In addition, the flow of the exhaust fume is also progressively slowed down as the exhaust fume flows from the first air chamber 203A into the second air chamber 203B via the gas duct 204 and the gas holes 205. In light of the alternate arrangement of the gas ducts 204, the flow of the exhaust fume is effectively slowed down such that the duration of the exhaust fume to remain in the air chamber is prolonged. On the one hand, the gas noise of the exhaust fume current is absorbed by the noise-deadening fiber 206. On the other hand, the back pressure in the muffler is increased as a result of the prolonged stay of the exhaust fume in the air chambers. In view of the fact that the stay of the exhaust fume in the air chambers tends to be excessively prolonged, and that the return pressure tends to excessive in intensity, the exhaust fume emission can not be easily attained; in addition, when the intensity of the return pressure in the muffler is greater than normal, the basic of the inlet vacuum of the combustion chamber becomes greater, thereby resulting in the premature ignition timing as well as the inefficient operation of the engine, and more heating of the engine as well as the engine knock.
As shown in FIG. 4, the U.S. Pat. No. 4,574,914 discloses an muffler 30 which has a long flat cross section and are provided at both ends thereof with an inlet 301 and an outlet 302. The muffler 30 is provided therein with three sets of air chambers 40. Each air chamber set 40 is formed of a cup-shaped stop piece 50 and a partition 60. The cup-shaped stop piece 50 is fastened at the upper and the lower edges thereof with the wall of the muffler 30 such that the stop piece 50 is fastened in the air chamber 40, and that the stop piece 50 is contiguous to the inlet 301, and further that the stop piece 50 is provided with two stop walls 501 extending from the center point toward other end. The two stop walls 501 are vertically provided at the tail end thereof with a stop edge 502. The partition 60 is contiguous to the outlet 302 and is separated from the cup-shaped stop piece 50 at an interval. The partition 60 is provided at both ends thereof with an extension wall 601, which is fastened with the wall of the muffler 30.
The partition 60 is provided at the center thereof with a gas hole 602. The air chamber 40 is located between the partition 60 and the cup-shaped stop piece 50. As shown in FIG. 5, when the exhaust fume is released by the engine to enter the muffler 30, the exhaust fume enters the first air chamber 40A via the space between the stop piece 50 and the muffler 30 due to the obstruction of the stop piece 50 of the first air chamber 40A. The exhaust fume circulates in the first air chamber 40A to form a gas eddy current for absorbing the gas noise of the exhaust fume. When the gas in the first air chamber 40A has reached the saturation point, the exhaust fume diffuses via the gas holes 602 of the partition 60 into the muffler 30 such that the exhaust fume is obstructed by the stop piece 50 of the second air chamber 40B, and that the exhaust fume circulates once again. The noise of the exhaust fume is progressively absorbed by the gas eddy currents formed in the subsequent air chambers. The flow of the exhaust fume is prolonged in the air chambers by the stop piece 50 and the partition 60 such that the pressure in the muffler is increased to prevent the entry of atmospheric air into the muffler and that the muffler remains in the state of discharging the exhaust fume at the interval of the gas explosion of each cylinder.
In view of the fact that the stop piece and the partition are of a long piece construction, they can be fastened only in the muffler of a long flat construction. The motor vehicles of different models or makers are provided with the round fastening holes due to more space of trunk, the motor vehicles must be provided with the round muffler.
In addition, the upper and the lower edges of the cup-shaped stop piece are fastened with the wall of the muffler. When the exhaust fume is discharged by the engine to enter the muffler, the volume of exhaust fume entering the first air chamber via the gap between the stop piece and the muffler is limited. As a result, the exhaust fume tends to deposit between the stop piece and the inlet at the time when an excessive amount of exhaust fume is generated by the engines of various horse powers. The exhaust fume emission can not be thus carried out in time.